1. Field of the Invention
The present invention relates to a sputtering apparatus and a thin film formation method, and in particular to a sputtering apparatus suitable for producing multilayer thin films having a clean interface.
2. Related Art
The area recording density of a magnetic disk has remarkably increased in recent years, and researches and developments are now made to realize the recording density of 100 Gbit/ in2. A magnetic recording medium is classified into a longitudinal (horizontal) magnetic recording and a perpendicular magnetic recording, and the former is now mainly adopted. The recording density of the longitudinal recording medium increases as the product of residual magnetic flux density (Br) and film thickness decreases, and therefore the film thickness has been made very thin in order to increase the recording density. However, since the crystal grain of a magnetic layer becomes smaller as the film is made thinner, thermal stability falls due to thermal fluctuation or thermal magnetization relaxation phenomenon which causes the super-paramagnetism transition in which the magnetization of micro magnets cannot be maintained at a room temperature. This is thought to be the limitation of the recording density of longitudinal magnetic recording media.
Accordingly, in order to break down the limitation due to the thermal stability and to realize higher recording density, the perpendicular magnetic recording media have been paid much attention and earnestly researched.
Both recording media usually comprise; a substrate made of glass, Al or the like, an underlying layer of NiP, NiAl or the like formed thereon in order to control the crystal orientation of a magnetic recording layer or to increase the mechanical strength of substrate when a soft substrate like Al substrate is used, single- or multi-recording layers, and a passivation layer. The multilayer film is generally formed using an in-line type manufacturing apparatus.
The in-line type manufacturing apparatus is composed of a load lock chamber to load and unload a substrate on/from a carrier, a pretreatment chamber to carry out cleaning or heat-processing of the substrate, an underlying layer forming chamber, a plurality of magnetic recoding layer forming chambers which have the number of sputtering chambers corresponding to the number of magnetic recording layers, and a passivation layer forming chamber. There is installed a gate valve between every two chambers. A transportation rail on which the carrier moves is built in every chamber. The substrates are held by the carrier and transported to each chamber one by one along the rail.
First, a plurality of substrates are loaded on the carrier in the load lock chamber and transported to the pretreatment chamber. In the pretreatment chamber, the substrate is heat-treated in order to remove contaminations such as water adhering to the substrate, or in order to make uniform the crystal orientation and the grain size of the underlying layer which affect the crystal growth of the magnetic recording layer and to optimize the coercive force of the magnetic recording layer. Moreover, in order to deposit the magnetic recording film at an optimum temperature, the substrates are heated to a temperature higher than the temperature for deposition, allowing in advance for the temperature drop during transportation. In the case of, for example, a CoCrPt magnetic recording film, the maximum coercive force(Hc) is obtained at the temperature range of 200–230° C. as is apparent from the graph of FIG. 7 which shows the relationship between the coercive force of film to be formed and the film forming substrate temperature. Therefore, the substrate is usually heated to 280° C. or less so that the substrates are in the above-mentioned temperature range when they are transported into the magnetic recording layer forming chamber, and that, in addition, the underlying layer such as NiP would not be magnetized. The substrate can also be cleaned by the sputter-etching there.
Then, the carrier is successively transported to the underlying layer forming chamber, one or more magnetic recording layer sputtering chambers, and the passivation layer forming chamber to form respective layers with a predetermined thickness on the substrates. After that, the carrier returns to the load lock chamber where the processed substrates are detached from the carrier and unprocessed substrates are loaded to the carrier.
Thus, a plurality of carriers are sent from and returned to the load lock chamber through the pretreatment chamber and the layer forming chambers to carry out the continuous production of magnetic recording media.
However, the method for forming a multilayer film by transporting the substrates to a plurality of chambers to form respective layers is disadvantageous that the residual gas in a vacuum adsorbs on the film surface during the substrate transportation and deteriorates magnetic characteristics as a result of the impurities mixing and the oxide layer formation at the interface.
In the case of the multilayer film of very thin layers, especially such as a magnetic recording film composed of repetitions of bilayer of Co and Pd in which each layer has a thickness of 1 nm or less, the residual gas influences remarkably the characteristics, which may make it impossible to obtain desired magnetic characteristics. In the case of, e.g., CoCr longitudinal magnetic recording media, it was found that adsorbed gas made the crystal grain of the film deposited thereon finer, and diffused into the magnetic recording layer to decrease the coercive force since the formation of the magnetic isolation structure of the crystal grains which is necessary for the noise reduction and which is attributed to the Cr segregation to the grain boundary is inhibited.
Furthermore, the disadvantage of the temperature drop during the substrate transportation cannot be avoided, and therefore it is difficult to set the substrate temperature at an optimum value in respective film forming chambers. That is, in order to manufacture a magnetic recording medium having higher characteristics, each magnetic recording layer should be formed at an optimum temperature for various materials and constructions of the film. However, it was difficult to meet such demands with prior art apparatuses.
In the case of forming multilayer films composed of tens of layers such as a Co/Pd multilayer magnetic film, the substrates are transported to many process chambers. As a result, the surface is contaminated with residual gas during transportation. In addition, a huge floor space is requested for the apparatus since its size is extremely increased.
Although the disadvantages of prior art apparatus and film forming method have been described for the magnetic disks as an example, similar problems are also anticipated to occur for a variety of elements or devices using magnetic thin films such as a magneto-resistive (MR) head for read/write operation, and multilayer devices or elements composed of various materials other than magnetic materials.